Polyurethane foams, formed by the reaction of a polyisocyanate with a polyhydroxyl-containing compound in the presence of a suitable catalyst, are widely accepted as padding materials for cushions in furniture, automobiles and the like. Polyurethane foams are also used in sponges, personal care and hygiene items and as specialty packaging materials.
The use of a polyol in the preparation of polyurethanes by reaction of the polyol with a polyisocyanate in the presence of a catalyst and perhaps other ingredients is well known. Conventional polyols for flexible polyurethane foams, such as slab urethane foams, are usually made by the reaction of a polyhydric alcohol with an alkylene oxide, usually ethylene oxide and/or propylene oxide, to a molecular weight of about 2,000 to 5,000 and above. Polyols have been modified in many ways in attempts to improve the properties of the resulting polyurethane, for example, by using a polymer polyol as the polyol component. Conventional polyols may be used as the dispersing media or base polyol in these polymer polyols.
For example, dispersions of polymers of vinyl compounds such as styrene, acrylonitrile or a mixture of the two (abbreviated as SAN), or of polyurea polymers, such as those prepared from toluene diisocyanate (TDI) and hydrazine in conventional polyols have been included to improve the properties of the polyols, and thus, the properties of the resulting foam. Polyurethane foams with higher load bearing properties (ILD-indentation load deflection, and CFD-compression force deflection) may be produced in this manner. It would be desirable if polymer polyols could be prepared which would be stable and have low viscosities. Stability is important to the storage life of the polyols before they are used to make the polyurethane foams. The tendency of polymer polyols to undergo phase separation if they are not stabilized is well known. Dispersants are often used to help keep the polymers in the dispersion. Low viscosities and small particle sizes are also important in a good quality polyol to permit it to be pumped easily in high volume foam producing equipment.
It would further be desirable if styrene/acrylonitrile polymer polyols could be synthesized which would have large SAN ratios. The substitution of styrene for acrylonitrile in these polymer polyols helps prevent discoloration during the cure of the polyurethane, and also helps improve flame retardability of the resultant foams. However, the stability of the polymer polyols decreases with increasing styrene to acrylonitrile ratios. Viscosity and particle size are also typically adversely affected by high styrene contents.
It is known to polymerize monomers in the presence of polyols to make dispersants in turn used in polymer polyol preparation. For example, International Publication No. WO 87/03886 and U.S. Pat. No. 4,745,153 teach the homo- or co-polymerization of vinyl-terminated polyol adducts alone or together with an ethylenically unsaturated monomer or monomer mixture in the presence of an active hydrogen-containing compound as a solvent, and their use as preformed dispersants. Preformed stabilizers comprising a copolymer of an anchor portion consisting of an ethylenically unsaturated monomer or mixture of such monomers and a solvatable portion consisting of a propylene oxide polymer are described in U.S. Pat. Nos. 4,242,249 and 4,350,780. Only monofunctional materials are used in these products.
See also U.S. Pat. Nos. 4,327,005 and 4,334,049 to Ramlow, et al., which teach alkylene oxide adducts of styrene/allyl alcohol copolymers as preformed stabilizers for polymer polyols. The stabilizers may take the form of a graft copolymer dispersion or a finely divided solid polymer.
It is known in the art that dispersants for polymer polyols can be prepared by coupling polyols together through their hydroxyl groups. For example, U.S. Pat. No. 4,357,430 teaches that a coupled polyol consisting of the reaction product of a polyol with a polyisocyanate is suitable as a dispersant. U.S. Pat. No. 4,831,076 discloses a modified polyol obtained by the reaction of a polyol with a coupling agent having at least two functional groups which are reactable with the hydroxyl groups on the polyol which is used as a dispersant for polymer polyols.
It is well known in the art that high styrene content polymer polyols are desirable, but difficult to prepare in stable form. It has been discovered that the polymerization reaction product of polyethylenically unsaturated monomers in a base polyol may be useful themselves as dispersants in preparing polymer polyols that have relatively high styrene contents, but which also had good stability, small particle sizes, and low viscosity as well.